Step-change gearbox

ABSTRACT

Multi-speed step-change transmission for commercial vehicles having an one input shaft, a main shaft placed in an axial extension, one countershaft parallel thereto and one intermediate shaft parallel to the two shafts for the reverse gear and the shafts have gear wheels forming the ratio steps of the transmission. The sum of the tip radii of the intermediate gear ( 3 ) for the reverse gear and of the main shaft gear ( 1 ) for the first gear is smaller than the axial separation (a) between the main shaft ( 5 ) and the intermediate shaft ( 6 ).

FIELD OF THE INVENTION

The invention relates to a multi-speed step-change transmission,especially for commercial vehicles, having one input shaft and one mainshaft situated in an axial extension of the input shaft, onecountershaft disposed parallel to the main shaft and, situated parallelto said two shafts, one intermediate shaft of the reverse gear.

BACKGROUND OF THE INVENTION

Such step-change transmission are widely known. The Applicant's DE A 4429 546 thus describes a multi-speed step-change transmission wherein themain shaft and the countershaft are provided with gear wheels engagedwith each other and forming the ratio steps of the transmission. Thecountershaft itself is divided, both parts of the countershaft beingoptionally connectable with the main shaft; in the normal forward gearsone part of the countershaft remains uncoupled. Such transmissions canparticularly be used in commercial vehicles having nine or ten gears.

In multi-speed step-change transmissions for commercial vehicles, theteeth of the countershaft for the reverse gear are often identical withthose of the first gear, there necessarily resulting a somewhat quickerreverse gear with a velocity increase amounting to about 5% to 10%.Therefore, these equal countershaft teeth are selected in order toproduce the two countershaft teeth in one operation and with the sametool or the same tools. But the quicker ratio in reverse gear results inan overall gear ratio of the transmission caused thereby. The requiredoverall gear ratio of the transmission results from the marginalconditions of a creep velocity as low as possible in the first gear andin the reverse gear at idling rotational speed of about 600 r.p.m. and amotor rotational speed as favorable to consumption as possible of about1200 r.p.m. to 1500 r.p.m. at a maximum speed which is of about 85 km/h.However, as result of the given vagueness in reverse drive, there is asa rule desired a lower creep velocity in the reverse gear than in thefirst gear, for example, <2.5 km/h in reverse gear compared to <3.0 km/hin the first gear.

Transmissions have become known that make possible in the reverse gear aslower ratio than in the first gear. But those transmissions have thedisadvantage that different tools are required for producing thedifferent teeth, which increases the production costs.

In the Applicant's German Patent Application No. P 199 04 479, atransmission has already been proposed which makes a slower creepvelocity in the reverse gear possible than in the first gearsimultaneously with a reduced overall gear ratio of the transmission andin which the same tools can be used in the production of the teeth sothat costs can be lowered in the production. In said transmission thegear wheel provided upon the main shaft for the first gear has the sameteeth as the gear wheel provided upon the main shaft for the reversegear.

However, in this and the other known transmissions mentioned above it isnot possible that the intermediate gear for the reverse gear lie inaxial direction in the area of the gear for the first gear, since thesum of tip radii of the intermediate gear for the reverse gear and ofthe main shaft gear for the first gear is greater than the axialseparation of the main shaft from the intermediate shaft for the reversegear.

The problem on which this invention is based is to provide a step-changetransmission which, in axial direction, needs less installation spacethan the step-change transmissions known already and which has a highertransmission ratio in reverse gear than in the first gear simultaneouslywith reduced overall gear ratio of the transmission and where the sametools for the production of the teeth make lower production costspossible.

On the basis of a step-change transmission of the kind specificallymentioned above, said problem is solved with the feature stated in thecharacteristic part of the main claim; an advantageous embodiment isdescribed in the sub claim.

SUMMARY OF THE INVENTION

According to the invention, it is, therefore, provided that the teeth ofthe gear train from first gear and reverse gear be configured so thatthe intermediate gear for the reverse gear can use, in axial direction,the same space as the main shaft gear for the first gear. Furthermore,the tooth geometry is identical on the countershaft for the first gearand the reverse gear.

The configuration is especially advantageous for transmissions where themain shaft gear for the first gear and the main shaft gear for thereverse gear are disposed directly side by side, that is, no shiftingset or the like is situated between the two gears.

More precisely said, the sum of the tip radii of the intermediate gearfor the reverse gear and of the main shaft gear for the first gear issmaller than the axial separation between the main shaft and theintermediate shaft for the reverse gear. It is thereby possible that theengagement between countershaft for the reverse gear and intermediategear for the reverse gear occurs in an axial plane different from thatof the engagement between the intermediate gear for the reverse gear andthe main shaft gear for the reverse gear.

The inventive configuration offers the further advantage that noaltering stress due to root foot bending of the intermediate gear forthe reverse gear occurs so that less space is needed in axial direction.The required tooth width between countershaft for reverse gear andintermediate shaft for reverse gear is not included in the total lengthof the transmission as long as the following condition is met: width ofthe first gear≧width of the reverse gear VW/ZW.

In reverse gear, a higher transmission ratio than in the first gear ispossible with simultaneously reduced overall gear ratio of thetransmission; for the first gear and, for the reverse gear, equal teethare possible upon the countershaft, it being possible to design shorterthe teeth upon the countershaft, that is, only as wide as it is neededfor the first gear.

The production costs are kept low because of the equal tools forproducing the teeth (equal module and equal helix angle of the teeth ofthe first gear and of the reverse gear). The inventive configurationthus combines the advantages of the known technical solutions withouttheir disadvantages.

BRIEF DESCRIPTION OF THE DRAWING

The invention will now be described, by way of example, with referenceto the accompanying drawings in which:

FIG. 1 shows a longitudinal section through one of part of the inventivestep-change transmission.

FIG. 2 shows a side view of the gear wheels situated in this place.

DETAILED DESCRIPTION OF THE INVENTION

It is provided according to the invention that the sum of the tipdiameters of the intermediate gear 3 for the reverse gear$\frac{daR}{2}$

and of the main shaft gear 1 for the first gear $\frac{da1}{2}$

be smaller than the axial separation a between main shaft 5 andintermediate shaft 6. It is thereby possible that the engagement betweenreverse gear countershaft 4 and the intermediate gear 3 for the reversegear occurs in an axial plane different from the engagement between theintermediate gear 3 for the reverse gear and the main shaft gear 2 forthe reverse gear.

It is provided according to the invention that the sum of the tip radiiof the intermediate gear 3 for the reverse gear $\frac{daR}{2}$

and of the main shaft gear 1 for the first gear $\frac{da1}{2}$

be smaller than the axial separation a between main shaft 5 andintermediate shaft 6. It is thereby possible that the engagement betweenreverse gear countershaft 4 and the intermediate gear 3 for the reversegear occurs in an axial plane different from the engagement between theintermediate gear 3 for the reverse gear and the main shaft gear 2 forthe reverse gear.

REFERENCE NUMERALS

1 main shaft gear of first gear

2 main shaft gear of reverse gear

3 intermediate gear for reverse gear

4 countershaft

5 main shaft

6 intermediate shaft

What is claimed is:
 1. A multi-speed step-change transmission having one input shaft and one main shaft (5) situated in an axial extension of the input shaft, one countershaft (4) disposed parallel to the main shaft (5); the main shaft (5) and the countershaft (4) having gear wheels forming ratio steps of the transmission including a main shaft gear (1) for first gear and a main shaft gear (2) for reverse gear on the main shaft, one intermediate gear (3) for the reverse gear upon an intermediate shaft (6) and teeth for the reverse gear and the first gear upon the countershaft (4); wherein a sum of a tip radius (daR/2) of the intermediate gear (3) for the reverse gear and a tip radius (da1/2) of the main shaft gear (1) for the first gear is smaller than an axial separation (a) between the main shaft (5) and the intermediate shaft (6).
 2. The step-change transmission according to claim 1, wherein a geometry of the teeth upon the countershaft (4) is identical for the first gear and for the reverse gear. 